The production of many commercially valuable metals, or metal compounds, from mineral ores includes a process step of digesting the ore with a mineral acid such as hydrofluoric acid. The digesting step is utilized to convert metal species in the mineral ore to metal species which are soluble in aqueous systems so that the metal values may be separated out by selective extractions or the like.
In a typical process, mineral ore concentrates containing tantalum and niobium are conventionally decomposed with hydrofluoric acid (HF) or mixtures of hydrofluoric acid and sulfuric acid (HF/H2SO4). The tantalum and niobium heptafluoro complexes formed are then separated and purified by solvent extraction.
More particularly, in a conventional process for producing tantalum pentoxide (Ta2O5), the tantalum fraction from the ore decomposition is stripped into the aqueous phase and tantalum pentoxide is precipitated using ammonia and recovered by filtration. Niobium pentoxide may be produced in a similar fashion.
Commercial schemes for the extraction and separation of tantalum and niobium values from beneficiated ores or from tin slags are described in detail in U.S. Pat. Nos. 2,767,047; 2,953,453; 2,962,372; 3,117,833; 3,300,297; 3,658,511; 3,712,939 and 4,164,417. A general discussion of other ore process schemes is found in Extractive Metallurgy of Niobium, Tantalum and Vanadium, INTERNATIONAL METALS REVIEW, 1984, VOL. 29, NO. 26, BB 405-444 published by The Metals Society (London) and in The Encyclopedia of Chemical Technology, 3rd Ed., Vol. 22 pp. 547-550.
The processes described above, and in particular the tantalum/niobium production processes, produce digested ore residues which include a number of different metal values including tantalum and niobium. U.S. Pat. No. 5,384,105 relates to a process for recovering tantalum/niobium residues from highly fluorinated ore materials by contacting the materials with a mineral acid mixture which includes boric acid (H3BO3).
The process of the present invention provides a means for solubilizing metal values from ore residues, such as the ore residues produced by a conventional tantalum/niobium oxide production process to permit separation and recovery of various metal values prior to further processing of the ore residues.